Edge form assembly for pressing of articles

ABSTRACT

AN APPARATUS FOR USE IN THE PRESSING OF ARTICLES COMPRISING A VERTICALLY DISPLACEABLE EDGE FORM COMPONENT FOR THE MOULD WALLS WHICH COMPONENT CAN BE HELD MAGNETICALLY TO A LOCATING STRUCTURE DURING PRESSING. IN SOME EMBODIMENTS OF THE INVENTION, THE COMPONENT IS ASSOCIATED WITH A STATIONARY EDGE FORM COMPONENT ALSO PROVIDING PART OF THE MOULD WALLS. THE MAGNETS MAY BE PERMANENT MAGNETS, PERMANTNE ELECTROMAGNETIC CHUCKS, SWITCHABLE PERMANENT MAGNETIC CHUCKS OR ELECTROMAGNETS.

June 6, 1972 M. A. MALET ETAL EDGE FORM ASSEMBLY Fon PRESSING OF ARTICLES 7 Sheets-Sheet 1 Filed Nov. 25, 1969 F /G.2A.

June 6, 1972 A. MALET ETAL EDGE FORM ASSEMBLY FOR PRESSING OF ARTICLES 7 Sheets-Sheet 2 Filed NOV. 25, 1969 V IL i l l -llnlnl 'F/G.5A.

\\\\ FIG. 8B.

June 6, 1972 -r EI'AL EDGE FORM ASSEMBLY FOR PRESSING OF ARTICLES Filed Nov. 25, 1969 '7 Sheets-Sheet S June 6, 1972 A. MALET ETAL 3,667,880

EDGE FORM ASSEMBLY FOR PRESSING OF ARTICLES Filed Nov. 25, 1969 7 Sheets-Sheet 4.

) l l Y/////7/////////// ////////////J////// I //////////////Z//@ a A &

m jF/G.6. I38

ISOLATOR 200/250 SWITCH VOLT SUPPLY CONTROL SWITCH 53$; EL c oNm /34 UNIT FIG. 7. B2

SILICON 2-2%%% C5??? RIVER CONTACTS I dc l -ac smcoN CONTROLLED RECTIFIER June 6, 1972 M -r ETAL 3,667,880

EDGE FORM ASSEMBLY FOR PRESSING 0F ARTICLES Filed Nov. 25, 1969 7 Sheets-Sheet 5 June 6, 1972 M -r ETAL 3,667,880

EDGE FORM ASSEMBLY FOR PRESSING OF ARTICLES Filed Nov. 25, 1969 '7 Sheets-Sheet 6 F I6. 70. a?

XI F 7 75 76 72 l/ 1/ l 5 Pin l 80 10 92 u E 9 l: i I 32 m i I 3 m" H 4 m 34 32 F g l u i 34 I0 1 I 76 m a, 7/ 2 72 76 F I G 9 3 82 June 6, 1972 MALET ETAL EDGE FORM ASSEMBLY FOR PRESSING' 0F ARTICLES Filed NOV. 25, 1969 7 Sheets-Sheet 7 sGI v 3 a a am a mEmG w\\\\\\\\\\\\\\\\\\\\ w R mm MM m United States Patent 3,667,880 EDGE FORM ASSEMBLY FOR PRESSING 0F ARTICLES Michael Anley Malet and David Leslie Hills, Watford, England, assignors to National Research Development Corporation, London, England Filed Nov. 25, 1969, Ser. No. 879,879 Claims priority, application Great Britain, Nov. 26, 1968, 56,110/ 68 Int. Cl. 1328b 3/00 US. Cl. 425-3 16 Claims ABSTRACT OF THE DISCLOSURE An apparatus for use in the pressing of articles comprising a vertically displaceable edge form component for the mould walls which component can be held magnetically to a locating structure during pressing. In some embodiments of the invention, the component is associated with a stationary edge form component also v providing part of the mould walls. The magnets may be permanent magnets, permanent electromagnetic chucks, switchable permanent magnetic chucks or electromagnets.

I This invention relates to the pressing of articles, and in particular to the pressing of concrete articles such as panels of concrete, reinforced or otherwise, for building or engineering purposes.

A process for pressing concrete articles is already known in which a wet concrete mix is fed to a mould in which the mix is levelled, for example by vibratory means; the mould is then placed between the platens of a press, one platen at least being arranged to enter the mould, and pressure is applied between the platens to force water out of the mix. It is desirable in that case that the press should be made versatile so that it could be usedfor the production of different sizes of panel, and this requirement will usually apply whatever the material being pressed.

According to one aspect of the present invention, an edge form assembly for use in a pressing process comprises a magnet, an edge form component displaceable in the direction of pressing and adapted to present one or more mould surfaces for the material to be pressed, and one or more locating surfaces adapted to locate the edge form component against pressure exerted on the component by the material during pressing, whereby operation of the magnet urges the component towards said one or more locating surfaces. The edge form component may have at least a portion of magnetic material and is preferably wholly of magnetic material.

In one embodiment, the displaceable edge form component co-operates with a stationary edge form component locked against displacement in said direction of pressing and also adapted to present one or more mould surfaces in the pressing process. The stationary edge form component may have at least a portion of magnetic material, or may be of non-magnetic material.

In one arrangement, the stationary edge form comprising a vertically displaceable edge from the comas in operation of the magnet means to urge or assist in urging the displaceable edge form component towards said one or more locating surfaces. Conveniently, the stationary edge form component co-operates with locating surfaces for the displaceable component to define a recess to accommodate the lower edge of the displaceable component during the pressing process.

The locating surfaces may be at least in part provided by a beam positioned adjacent the displaceable edge form component, and in one embodiment the displaceable edge ice form component is constituted by a castellated strip and the locating surfaces. for said component are in part provided by the beam and in part by a number of blocks spaced apart one from the other in abutment with the beam.

Alternatively where the displaceable edge form component is constituted by a castellated strip, the locating surfaces for this component may be provided by the stationary edge form component which is constituted by a second strip similarly castellated when Viewed in plan.

If desired, the displaceable edge form component(s) and/ or locating surfaces are designed to accommodate reinforcement members projecting from the material to be pressed.

In variations of the above described embodiments the displaceable edge form component is provided with one or more projection(s) arranged to serve as inserts for the material to be pressed. The projections may be of light plastics material such as Tufnol or Paxoline or they may be aluminium for example. The projections may be hollow and can then be formed of steel plate for example.

Where the locating surfaces are at least in part provided by a beam then the beam conveniently incorporates the magnet means. The magnet means may be constituted by a permanent magnet or by one or more switchable permanent magnetic chucks, or by one or more electromagnets, or by one or more switchable permanent electromagnets.

The invention also includes edge formers for use in one or more of the edge form assemblies according to the present invention. The invention also extends to the components of these edge formers.

According to another aspect of the present invention a method of forming an article from a concrete mix between the upper and lower platens of a press includes the steps of providing a mould bottom, providing one of the edge form assemblies of the present invention on said mould bottom to provide a boundary wall for the material to be pressed, providing the other boundary walls for the material, introducing said mix within the region enclosed by said boundary walls, providing relative motion between said upper and lower platens to press the article from the material and reduce the height of the edge form assembly, and removing excess water from the mix during pressing.

In order that the invention may be more fully understood, embodiments thereof will now be described, by way of example, with reference to the accompanying drawings, of which:

FIG. 1 shows a vertical section through an edge form assembly in accordance with the present invention as it will appear after completion of the pressing process. The

top platen of the press is shown withdrawn;

FIG. 2A shows a vertical section through another edge form assembly in accordance with the present invention as it would be immediately prior to the introduction of the material into the mould;

FIG. 2B shows a plan view of part of the edge form assembly shown in FIG. 2A;

FIG. 3 shows a vertical section through a further edge form assembly in accordance with the present invention as it would appear on completion of the pressing operation;

FIG. 4 shows a vertical section through yet another edge form assembly in accordance with the present invention, also illustrated as it would appear on completion of the pressing operation;

1 FIG. 5A is a vertical section taken along the line A-A in FIG. 5 B

FIG. 5B is a back view (on an enlarged scale) of the FIG. 1 assembly with part of the beam casing removed to show the use of permanent magnets in the beam;

FIG. 6 is a horizontal section (on an enlarged scale) taken along the line VI-VI in FIG. 2A and illustrating the use of permanent electromagnetic chucks as the magnet means;

FIG. 7 shows a control system for the electromagnet chuck arrangement of FIG. 6;

FIG. 8A is a side view (on an enlarged scale) of the beam used in the FIG. 3 assembly and illustrates the use of switchable permanent magnet chucks as the magnet means;

FIG. 8B is a vertical section taken along the line B-B in FIG. 8A;

FIG. 9 is a plan view of a complete mould in accordance with the present invention;

FIG. 10 shows a modification of the FIG. 9 mould for the production of an alternative type of panel;

FIG. 11A is a vertical section (on an enlarged scale) taken along the line XIXI of FIG. 9 assembly;

FIG. 11B is a similar section illustrating an alternative type of mould bottom; and

FIG. 12 is a plan view of an alternative (swinging-link) arrangement for the beams.

Thus referring first to FIG. 1, the edge form assembly there illustrated includes a beam 10 supported by a composite mould bottom 90 which is positioned on the bottom platen 11 of a press for pressing concrete articles. As shown, the mould bottom 90 comprises a fine perforated plate 504 V holes in a V thick steel plate), and an apertured mould bottom 506 located on the platen 11 which is grooved as shown in the figure. The beam 10 is separated from the supporting surface of mould bottom 90 by a sheet of filter paper 502 e.g. Kraft 500. The beam 10 is one of four such beams providing an adjustable rectangular frame around the mould space and it incorporates a plurality of permanent pot magnets 14 staggered vertically along the length of the beam. The edge form component is constitued by a former" 16 of V plate steel having a vertical width somewhat greater e.g. 3 mm. than the corresponding dimension of the beam 10 and extending parallel to the beam to present all or part of a mould surface 18 for one wall of the article to be pressed. When the former is raised above the mould bottom 90 the inside face 22 of the beam 10 presents the" the press which has V-shaped grooves 510. The mould top 508 is of identical construction to the mould bottom 90 and corresponding reference numerals have been used in both cases for the similar parts.

As shown in FIG. 1, the former 16 may be provided with a number of slots such as slot 28 extending vertically upwards from its lower edge to accommodate metal reinforcement 30 projecting beyond the moulded face of the article. Clearly in such a case the beam 10 must be provided with appropriate recesses 31 extending downwardly from the upper surface of the beam to accept the reinforcements 30 and allow the pressed article to be lifted from the mould bottom 90 once the pressing process has been completed without the necessity of first withdrawing the beam by the amount of reinforcement 30 in the recess 31.

FIG. 5A is a vertical section taken in a plane parallel to that of FIG. 1 along the line A-A of FIG. SE to show the detailed construction of the edge form assembly between adjacent recesses 31 of the beam 10. FIG. 5B is a side view of the beam 10 looking inwards toward the mould and with the back plate 32 of the beam casing removed more clearly to show the withdrawal system for the pot magnets incorporated in the beam.

As will be seen from FIG. 5A, there are a plurality of such magnets 44 arranged in vertically staggered faslnon along the length of the beam and each comprises a cylindrical mild steel shell 42- housing a powerful permanent magnet 44. The shell 42 is apertured at surface 22 of the beam 10 to enable the magnet 44 to engage directly with the edge former 16 when the magnet is in the operative position illustrated. At its other end the shell 42 is centrally apertured to accommodate an actuating rod 46 carrying a stop nut 48 which is urged against stop girders 52 by Belleville washers 54. Stop girders 52 are connected together by actuating plates engaged by the cams 60 of a cam shaft 62 passing down the length of the beam 10. The back plate 32 of the casing is apertured at 56 to allow axial movement of the rods 46 against the action of the Belleville washers.

A plan view of the complete mould is shown in FIG. 10 with the mould top removed. Thus referring now to FIG. 10, rigid casings 71 are secured at opposed corners of the mould bottom and the racks 72 of a rack and pinion actuating system extend into these casings where they are engaged by appropriate actuating pinions. Each rack 72 carries a number of spaced locking wedges 73 on is upper surface and longitudinal movement of the rack moves these wedges into and out of locking engagement with corresponding channels 74 in the base blocks 75 of a number of stops 76 for the associated beam 10. The axial extension of the steps 76 may be increased by fitting extensions 77 where necessary and fine control is provided by screw adjustments 78.

Pairs of adjacent base blocks 75 are interconnected by links 79 which provide pulling slots 80 for engagement by any suitable withdrawal mechanisms eg by a series of ganged bell-crank members having end pins located in the slots 80.

The locking wedges 73 are slightly inclined to the engaging surfaces of the channels 74 so that as the wedges move into the channels 74 of the base blocks, they force the base inwards by a small distance (cg. inch) towards the mould space, and when they are removed the base blocks (and hence also the stops 76) are withdrawn by this small distance in a closely controlled fashion.

In the example illustrated in FIG. 10 the lengths of the beams 10 are such that the stops 76 for the shorter beams must be associated with spacer elements 81 connecting the beams with a pusher girder 82 secured to the stops 76.

Prior to commencement of the pressing operation proper, the beams 10 are adjusted to provide an appropriate mould for the article to be pressed. This is done with the stops 76 using extensions and spacer elements where necessary as above described. The edge formers are then raised to a suitable height consistent with the articles to be pressed e.g. to have their top edges nine inches above the mould bottom where a final panel width of eight inches is required. After this the moulding faces presented by the edge formers and the beams 10 are coated with a suitable release agent e.g. Noxcrete (marketed in the USA. by the Noxcrete Company of Omaha, Nebr. and in Great Britain by the Crete Company Limited). Cam shafts 62 are next rotated through to put the pot magnets in the operative positions illustrated in FIG. 5A where they act to hold the edge formers 16 against locating surfaces 22. Concrete mix 26 is then introduced into the mould space. A typical mix might be cement, crushed limestone aggregate having particles of sizes between and dust, and crushed limestone aggregate having particles of sizes between and 7 in the proportions 1:2.4: 1.2 by weight, the ratio of water to cement in this mix being 0.7:1 by weight. The bottom tapered edges of the formers 16 will be at the position indicated by reference numeral 20'.

The concrete filling is next covered by an appropriate sheet of filter paper and the bottom platen of the press is moved underneath the top platen of the press which is actuated to bring the mould top into engagement with the filter paper and the mould edges 24. Pressure is then applied between the platens to depress the formers 16 and compress the mix, excess water being expelled through the perforated plates, the mould bottom 90' and the grooves in the top and bottom platens of the press. Details of the basic concrete pressing process may be had from co-pending UK. patent application 6,874/ 66 published as No. 1,179,405. During the pressing process, the formers 16 will slide across the locating surface 22 presented by the beam -against which they are held initially by the attraction of magnets 14 and the pressure exerted by the concrete mix. The tapered lower edges of the formers will move easily through the mix for a preselected time at a preselected pressure after which downward movement of the top platen is ceased. Compression of the mix has been complete when this stage is reached and the top edge of the formers will now be at a position 24 level with the top surface 28 of the pressed concrete article. Typically for an eight inch pressed panel thickness and the mix above described by way of example, pressing will be carried out at a pressure of 400 p.s.i. for about one minute during which about half the original water content will be expelled.

To demould the article, the top platen is withdrawn with the attached mould top and the bottom platen is moved to one side still supporting the mould and the pressed article. Then with the magnets 14 still operative, the actuating pinions are operated to move the racks 72 and release the locking wedges 73 from the channels 74 thereby causing a small controlled withdrawal (e.g. l4 inch) of the beams and their edge formers as herein'before described. Withdrawal is completed using the withdrawal slots 80. Once demoulded, the article may be lifted from the mould bottom with a vacuum pad and transferred to an appropriate casing station.

FIGS. 2A to 4 show alternative edge form assemblies to that illustrated in FIG. 1 but parts of the various assemblies have been given the same reference numerals in the different figures whenever their construction is similar or substantially identical. Thus referring next to FIG. 2, there is shown an edge form assembly in which the former 16 of the first described embodiment has been replaced by a former 32 also of plate steel but castellated when viewed in plan (as shown in FIG. 2B). The locating surfaces 18 for this former are now provided not by the beam 10 as before, but by a second former 34 castellated in the same way as the first former and positioned against the vertical faces of the beam 10 and support blocks 35. As before there will be four such assemblies to define the four sides of the mould space.

The magnet means in this embodiment are provided by permanent electromagnet chucks 114. FIG. 6 shows a horizontal section taken on the line 66 of FIG. 2A and FIG. 7 shows an electronic control circuit for automatically magnetising and demagnetising the chucks. Thus referring now to FIG. 6, each electromagnetic chuck comprises an alloy magnet 116 incorporated in the beam 10 andsurmounted by an associated pole piece 118. Surrounding the magnet is a copper coil 120, through which direct current is passed to magnetize and demagnetize the assemblies.

The individual magnetic units are set in a series of recesses machined in a plate 122, of high permeability mild steel, which provides a rigid fluid-tight base. Fixed to the upper faces of the base is a top plate 124, which is made up from a series of high permeability mild steel strips 126 of various widths, extending for the length of the chuck, these strips being separated by brass spacers, also of various widths.

In the control circuit of FIG. 7, silicon controlled rectifiers 130 are used to control the main current and amplify signals which are originated in a transistorized electronic unit 132 which initiates the magnetizing or demagnetizing sequence according to the setting of the control switch 134. Other details of the control circuit will appear from FIG. 7.

A plan view of the complete mould assembly is shown in FIG. 9 and FIG. 11A shows a detail of the stop assembly used in FIG. 9 and also illustrates a variation in which the displaceable edge form is profiled with a projection 136 and the stationary edge form includes a projection 138 located on the mould bottom 90.

The stop assembly shown in FIG. 11A is identical with that already described with reference to FIG. 10 and the reference numerals in FIG. 11A therefore read on to the description of the FIG. 10 assembly.

It should be noted that the cast article is trapped between the projections 136 and 238 and hence to permit the slight expansion which usually takes place when pressure is released from the article, the demoulding process is varied by first making the magnets inoperative so that the displaceable edge former is free to rise and allow expansion of the trapped portion of the pressed article. The magnets are then reapplied to hold the edge formers on to the beams for withdrawal as already described with reference to the previous embodiment.

As far as the mould lay out is concerned (FIG. 9) this is basically very similar to the FIG. 10 assembly and corresponding reference numerals have been used. However one difference is that two of the beams 10 consist of a number of discrete elements 10 whose spacing can be varied e.g. where the use of edge forms of slightly different lengths is envisaged. Larger changes of mould width are made by removing or adding elements 10'. Naturally each width of panel requires its own edge formers of the correct linear dimensions. The mould has also been illustrated for providing the pressed panel with an appropriate window opening 91 which is marked out by edge formers 32, 34 and assocated corner beams 10" all having the general characteristics described with respect to the FIG. 1 assembly. The beams 10" are held in place by hydraulic rams 92 acting between the inner faces of the beam and a rigid core structure 93 magnetically secured to the mould bottom 90.

Clearly if an opening is not required in the panel then the arrangement described with reference to FIG. 9 can still be used if the parts for providing the opening are omitted.

FIG. 11A illustrates an alternative type of mould bottom to that used in FIGS. 1 and 2 and shown in FIG. 11B. The alternative mould bottom shown in FIG. 11A comprises a solid mould base 503, a inch grillage 505, a coarse perforated plate 507 6 inch holes in 7 inch plate), and a fine perforated top plate 509 ($416 inch holes in inch plate). The top plate carries within the mould space the usual filter paper 502.

It will be seen that the operation of this embodiment is substantially identical to that of the FIG. 1 assembly except that the magnets 14 are now made operative by energising coils instead of by displacement relative to the moulding surface. Thus, in brief, the edge form assemblies are arranged to provide an appropriate mould and the magnets 14 are energised to hold the stationary edge formers 34 and the displaceable inner formers 32 (positioned as shown in FIG. 2A) against their associated beams 10. After addition of a suitable release agent, concrete mix is then introduced into the mould space, and subjected to pressure between the press platens. Levelling and vibration will not usually be necessary if the mould is filled carefully. When pressing is completed, the top surface of the article and of the displaceable former 32 will lie in the same plane as the top edge of the stationary former 34 and the article is ready for demoulding and curing in the usual way.

The embodiment of FIG. 3 once again includes a displaceable former 36 and a stationary former 38 both of plate steel but in this case the vertical width of the displaceable former is only about half that of the pressed article, and the stationary former extends upwardly from 7 the mould bottom 90 to define at its upper end (together with the locating surfaces 22 of beam a recess 40 in which the lower edge of the former 36 moves during the pressing process. The figure shows the edge form assembly in place around the pressed article. Prior to the commencement of pressing the former 36 will have been in the position 36' indicated in chain lines.

The magnet means of this embodiment are provided by a permanent magnetic chuck comprising a plurality of pole pieces spaced apart along the length of the beam and each including a stationary component located in a grid within the beam 10. FIG. 8A shows an inside view of a chuck in accordance with this embodiment of the inven- 'tion'in which the displaceable pole components 150 are shown mounted in a top plate 152 which is displaceable longitudinally of the beam by a common actuating system comprising displaceable rack bar 154, pinions 156 and eccentrics 158. The stationary components 159 are mounted ina grid 160 and with the rack at one extremity of its travel the displaceable pole components line up with the stationary components and the path of the magnetic flux includes the edge formers and holds them against the locating surface of the beam 10. With the rack at the other extremity of its travel, the two sets of pole components are out of alignment and although the magnetic flux still passes through the base plate 162 and the grid 160, the magnetic circuit is closed not through the edge formers 36, 38 but through the top plate 152 and the displaceable pole components contained in this plate.

In the particular example of the embodiment shown, the stationary former 38 is provided with an inward projection 40. The projection 40 is preferably formed of some light material or if formed of a heavier material such as steel or aluminium, the projection is made hollow to reduce weight. Steel plate can be used for this purpose. Suitable lightweight materials for the projection are plastics materials such as resin impregnated fibres of the kind typified by Tufnol and Paxoline for example. The moving former 36 may also be provided with an inward projection at its upper end and if desired the bottom of the former 38 can carry or be associated with a further inward projection although the requirement for this latter projection preferably to be lightweight no longer applies since this projection will be supported by the bottom of the mould. In this example the beams 10 are withdrawn using the assembly of FIG. 9 or 10.

In a third embodiment of the invention shown in FIG. 4, the assembly includes a number of blocks such as block 42 secured to the vertical surface 22 of the beam 10 in spaced relationships to one another. The displaceable edge former in this embodiment is constituted by a former 44 having a continuous portion from which extend projections 46 located (when the article has been pressed) or partly located (prior to pressing) between a respective pair of the adjacent blocks. In this embodiment the magnet means 14 is provided by a conventional electromagnet.

Various modifications and combinations of the above described embodiments will be obvious to those skilled in the art. For example, Where two formers are used (as in FIGS. 2A and 2B for example), the one located nearer the beam 10 need not necessarily be of magnetic material. A suitable non-magnetic material might for example be brass, aluminium or a plastics material. Nor need the formers be plates. Indeed one suitable type of former is steel sheet filled with a structural filler such as lightweight or dense concrete.

Similarly the assembly of FIG. 3 for example could be modified by using castellated formers in place of the flat strips shown in FIG. 3.

The assemblies of FIGS. 2, 3 and 4 could also be modified on the lines of that illustrated in FIG. 1 to accommodate projecting reinforcements from the material to be pressed.

It is further pointed out that the edge form components need not be thin plates and in various modifications (not shown) of the illustrated arrangements, these' plates are replaced by components of much greater 'width e.g. 2 inches or so. If the displaceable component is so modified, it will usually have a tapered lower edge (similar to edge 20 in FIG. 1) to facilitate its passage through the material during pressing.

Again it is important to realise that the beams used in the assemblies of the various figures are all interchangeable provided of course that they are provided with the necessary slots 31 when used with exposed reinforcements as in the FIG. 1 arrangement or with blocks 42 when in the FIG. 4 arrangement etc. Apart from these obvious reservations however as to any slight modifications in detailed design which might be necessary, the beam of any one figure is equally suited for use in the embodiments illustrated in the other figuresfor example the FIG. 3 beam using switchable permanent magnetic chucks is equally suited for use in the assemblies of FIGS. 1, 2, 2A and 4. i

Similarly, the edge formers 44 and blocks 42 of the FIG. 4 assembly may for example be replaced by the edge formers 32, 34 of the FIG. 2 assembly and this allows an alternative withdrawal system to be used in which the edge formers are arranged with the short vertical edgeof one pair (32, 34) engaging with the long face of the preceding pair and withdrawal is elfected using a swinging link arrangement. An example of such an arrangement is shown in FIG. 12. Thus referring to this figure, mould 600 according to the present invention comprises an'outer frame 602 to which beams 10 carrying edge formers 3:2, 34 are attached by a plurality of swinging links 606. It will be seen that each pair of edge formers has one short end face abutting with a long face of the next pair, and an end portion of one of its long edge faces abutting with the short end face of another pair. The links 606 are pivotally connected to the frame 602 and the beams'ltl thereby allowing motion of the associated edge formers parallel to the adjacent limb of the frame, this movement being effected by hydraulic actuators 608 which are pivotally connected between the free end of the beam concerned and the opposite part of the frame. It will be appreciated, therefore, that the particular disposition of the edge formers and beams relative to one another allows them to be moved in such a way that the inner faces of the edge formers will always provide a closed boundary of substantially rectangular shape. The magnets in this case will be conventional electromagnets incorporated in the beams as previously described with reference to FIG. 4. Prior to commencement of pressing the frame 602 is located in the mould bottom and actuators 608 are operated to move beams '10 into their desired positions. The edge formers 32 are then located in their raised positions against the beams 10 and the electromagnets are energised to hold the edge formers in place. Concrete mix is poured into the space defined by the inner edges of the edge formers and when the mould space has been filled and the concrete levelled etc., if necessary, then the upper platen. of the press is moved downwards to compress the material in the mould as has been previously described in connection with the earlier figures. When the pressing operation is completed the upper platen is removed, the actuators 608 are operated to withdraw the beams 10 and free the edge formers 32, 34 from the edges of the pressed article. It will be appreciated that at least in its initial stage, the movement of the edge formers 32, 34 during withdrawal is substantially parallel to the sides of the pressedgr ticle thereby reducing the risk of damage being caused to the article by any adhesion which might otherwise occur between the still moist concrete and the edge formers. A release agent may of course also be used if desired.

This system also offers a convenient way of readily adjusting the size of the mould.

We claim: 1. An edge form assembly for use in a pressing process, said assembly comprising an edge form component which is displaceable in the direction of pressing and having oppositely disposed sides, at least one mould space for the material to be pressed being defined at least in part by a said side of said displaceable component, locating means presenting at least one locating surface in sliding engagement with an adjacent side of said edge form component, magnetic means being carried by said locating means and disposed on the side of said edge form component opposite to said mould space, said magnetic means having an operative condition in which said magnetic means will exert a force of attraction on said edge form component to urge said component towards said at least one locating surface and an inoperative condition, control means for disposing said magnetic means in each of said conditions.

2. An edge form assembly as claimed in claim 1 in which the edge form component has at least a portion of magnetic material.

3. An edge form assembly as claimed in claim 1 in which the displaceable edge form component cooperates with a stationary edge form component locked against displacement in said direction of pressing and also presenting at least one mould surface in the pressing process.

4. An edge form assembly as claimed in claim 3 in which the stationary edge form component has at least a portion of magnetic material and overlaps the displaceable edge form component whereby said stationary edge form component, on operation of the magnet means will assist in urging the displaceable edge form component towards said at least one locating surface.

S. An edge form assembly as claimed in claim 4 in which the stationary edge form component co-operates with locating surfaces for the displaceable component to define a recess to accommodate the lower edge of the displaceable component during the pressing process.

6. An edge form assembly as claimed in claim 1 in which the locating surfaces are at least in part provided by a beam positioned adjacent the displaceable edge form component.

7. An edge form assembly as claimed in claim 6 in which the displaceable edge form component is constituted by a castellated strip and the locating surfaces for the said component are in part provided by a number of blocks spaced apart one from the other in abutment with a back-up beam.

8. An edge form assembly as claimed in claim 3 in which the displaceable edge form component is constituted by a castellated strip and locating surfaces for this 10 component are provided by the stationary edge form component which is constituted by a second strip similarly castellated when viewed in plan.

9. An edge form assembly as claimed in claim 1 in which the displaceable edge form component is designed to accommodate reinforcement members projecting from the material to be pressed.

10. An edge form assembly as claimed in claim 1 in which the displaceable edge form component is provided with at least one projection arranged to serve as an insert for the material to be pressed.

11. An edge form assembly as claimed in claim 1 adapted to define an opening in the material to be pressed.

12. An edge form assembly as claimed in claim 1 in which the magnet means is constituted by at least one permanent magnet.

13. An edge form assembly as claimed in claim 1 in which the magnet means is constituted by at least one switchable permanent magnetic chuck.

14. An edge form assembly as claimed in claim 1 in which the magnet means is constituted by at least one electromagnet.

15. An edge form assembly as claimed in claim -1 in which the magnet means is constituted by at least one switchable permanent electromagnet.

16. An edge form assembly claimed in claim 1 in which said at least one locating surface is designed to accommodate reinforcement members projecting from the material to be pressed.

References Cited UNITED STATES PATENTS 2,487,019 11/ 1949 Eichelberger 26926 X 2,416,559 2/ 1947 Wilson 18Dig. 33 3,321,807 5/1967 OBrien 18-Dig. 33 3,195,207 7/1965 Fougea 18Dig. 33 3,545,044 12/1970 Rebovich et a1 1816 R 3,534,439 10/1970 Haas et a1. 1816 R 3,261,897 7/1966 Munk 1816 R X 3,063,122 11/1962 Katz 249-457 X I. SPENCER OVERHOLSER, Primary Examiner B. D. TOBOR, Assistant Examiner US. Cl. X.R. 425-l10, 352, 84 

